1. Field of the Invention
The present invention relates to fax transmissions involving an IrDA protocol and, more particularly, to a method and means that enables a fax modem (DCE) to request a certain mode, local or end-to-end, from a PC having a virtual data port (DTE) with which the modem communicates over an IR connection when the fax class is made active, that is, when a fax is being received or is to be transmitted.
2. Prior Art
In a fax communication system including a PC with a virtual data port (DTE) and a fax modem (DCE), having an infrared (IR) connection between them, the latest IrDA IrCOMM specification calls for the software (SW) flow control signals (XON/XOFF characters) to be handled locally in the DTE or the DCE when the software flow control is enabled, so that no SW flow control signals are transmitted between the DTE and DCE. This feature is necessitated by the fact that if these characters were sent over the connection, they would have an effect on the local flow control emulation at the remote end which would cause a drop in the overall throughput over the IR connection and could also cause deadlocks or data to be lost. A problem is posed by this feature, however, with a PC using legacy, i.e., existing, fax software that operates under the assumption that the SW flow control characters are being transmitted between the DTE and DCE. Although this problem is not visible with existing RS-232 based implementations, because the SW flow control signals are not stripped and made local therein, it does arise in the virtual serial case where such stripping occurs.
Protocol layers in a DTE and DCE with the IrCOMM functionality are shown in FIG. 1. The various protocol layers inside the DTE and DCE are supposed to be transparent to the user of the virtual communications resource, but these layers, nevertheless, are not totally transparent. They can cause certain buffering related delays that may have negative effects on some protocols; for instance, they may cause some timing critical protocols to fail. This kind of problem is typical in re-transmission based systems and it appears there is not much that can be done to avoid these effects.